AT&T announced Sunday it has agreed to lease or sell the rights to 9,700 cell phone towers for $4.85 billion to Crown Castle International, which provides infrastructure for broadcasting and mobile telecommunications.

Under the terms of the deal, Crown Castle will have the option to purchase 9,100 towers for $4.2 billion after the average lease term of 28 years expires. Crown Castle will also purchase about 600 AT&T towers immediately.

As part of the deal, AT&T will sublease network capacity on the towers for $1,900 per month tower. That arrangement will last at least a decade, with AT&T having the option of renewing it for up to a total of 50 years.

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AT&T also has the option of reserving additional capacity in the future. The telecommunications giant expects the additional capacity to help it meet the growing demand for mobile Internet services.

"This deal will let us monetize our towers while giving us the ability to add capacity as we need it," AT&T SVP Bill Hogg said in a statement. "And we'll get additional financial flexibility to continue to invest in our business, maintain a strong balance sheet and return value to our shareholders."

The deal is expected to close by the end of the year.

The Houston, Texas-based Crown Castle proves mobile coverage to substantially all of Australia's population and has a presence in most of the 100 biggest mobile markets in the US.